1. Field of the Invention
The invention relates to the damping of vibrations in building structures.
2. Background of the Invention
Building structures and their various elements are subjected to various forces which will induce vibrations in such structures. Some of these forces are of natural origin such as wind, earth tremors and earthquakes. However, such forces generally produce vibrations throughout the entire structure.
Other forces which induce vibrations in building structures arise internally such as those resulting from rapid or impulsive changes in loadings of ceilings and floors. Floors and ceilings of relatively long span frequently have given rise to impulsive response vibrations as a result of varied occupancy thereof, and these vibrations create unpleasant sensations in the occupants of such buildings. With the advent of lighter section beams and joists, such as the light open web steel joists of comparatively recent development, the occurrence of these vibrations has increased and have constituted a considerable problem to the building industry. In some buildings employing relatively long spans of open floors supported by relatively light section beams or open web joists the occurrence of such vibrations induced by one or several people moving from one portion to another of the floor has been sufficient to create most annoying sensations in other occupants of such floors.
Various methods have been proposed to meet the problem posed by these loading vibrations. One such method proposed has been to increase the cross section of the supporting beams and thus increase the stiffness of the entire structure. Another method has been to increase the thickness of the flooring or ceiling material installed on the beams, such as poured concrete, but this also requires a corresponding increase in the size of the supporting beams. Neither of these methods is desirable in that neither is economical of materials or expense in building. Another proposal has been to increase the number of vertical supports of floors and ceilings such as additional columns or partitions installed to decrease the overall spans covered. This again is an uneconomical solution and sometimes one which cannot be adopted when relatively large open areas are required. It has been suggested to coat one or more surfaces of the entire beams with a layer of viscoelastic material additionally backed by relatively stiff materials to afford a shearing action in the viscoelastic, but this has not been adopted because of its high cost and uneconomical use of building materials and labor.
The present invention provides a system or method for damping these disturbing vibrations by the use of viscoelastic materials in a manner which does not require the use of heavier sections of supporting members nor of heavier sections of flooring or ceiling materials. Neither does it require the application of viscoelastic and stiffening materials to the whole of supporting beams or joists either in the field or during manufacture. The present method allows economies to be made in the size and weight of construction materials used while at the same time effectively damping out dynamic vibrations in a simple, economical and novel system.